Summary The IBA has supported small breeding colonies of the near threatened Letter-winged Kite and more than 1% of the global populations of the congregatory Plumed Whistling-Duck, Grey Teal, Hardhead, Little Black Cormorant, Australian Pelican, Straw-necked Ibis, Eurasion Coot, Oriental Plover, Gull-billed Tern and Flock Bronzewing. The IBA also provides habitat for the near threatened Australian Bustard. The IBA is an ephemeral wetland system, and holds significant numbers of waterbirds only when inundated. When fully inundated, the IBA may support 500,000 to 1,000,000 waterbirds.

Site description The large ephemeral Lake Sylvester system is located on the Barkly Tableland 180 km north-east of Tennant Creek. The IBA comprises of Corella Lake, Lake de Burgh, Lake Sylvester, an unnamed basin to the west of Corella Lake, and a surrounding network of interconnected wetlands. It includes two semi-permanent freshwater billabongs, Corella Hole and Big Hole, which are located upstream from the deltas that mark the meeting points of Corella Creek and Corella Lake and Brunette Creek and Lake Sylvester, respectively. Corella Lake, Lake de Burgh and Lake Sylvester are ephemeral freshwater lakes. They are seasonally inundated, but can retain water for more than 12 consecutive months after substantial floods. At normal capacity, Corella Lake (10,000 ha), Lake de Burgh (30,000 ha) and Lake Sylvester (15,000 ha) are discrete water bodies. In wetter years, excess water from Corella Lake flows into the unnamed basin to the west (5000 ha), and all four basins can become full and connected. During exceptional flood events, such as that which occurred in 2001-2002, all water bodies present in the system can merge to form a single massive lake with an area of up to 200,000 ha. The Lake Sylvester system is situated on deep-cracking grey clay that supports sparse to open shrublands dominated by Northern Bluebush and Lignum, sparse to open woodlands and scattered specimens of Coolibah, stands of Belalie, tussock grasslands dominated by Rat's Tail Couch and Pepper Grass, carpet-like patches of Annual Verbine, and mats of the aquatic species Nardoo, Spiny Mudgrass and (infrequently) Potamogeton tricarinatus and Myriophyllum verrucosum (DEWHA 2007; R. Jaensch pers. comm. 2007).

Key Biodiversity At least 65 species of waterbird have been recorded in the Lake Sylvester system (Wetlands International unpublished data provided by R. Jaensch). Waterbirds recorded in notable but sub-threshold numbers include Freckled Duck (observed on all three named lakes, with up to 56 birds on Corella Lake, and breeding at Lake Sylvester; the only confirmed breeding locality in the Northern Territory), Great Egret (1000 pairs at Lake Sylvester in 2006), Intermediate Egret (1000 pairs at Lake Sylvester in 2006), Glossy Ibis (3000 pairs at Lake Sylvester in 2006, the largest documunted inland colony of this species in the Northern Territory and one of the largest documented colonies in tropical Australia), Oriental Pratincole (more than 15,000 individuals at Lakes Sylvester and de Burgh in 1993), Australian Pratincole (1350 individuals in 1995) and White-winged Black Tern (1700 individuals counted in 2002 but real total possibly many thousands). Little Curlew have been recorded in moderate numbers, but the species is difficult to survey and actual numbers are therefore likely to be globally significant (Jaensch and Bellchambers 1997; R. Jaensch pers. comm. 2007). Sub-threshold numbers of Nankeen Night-Heron, Royal Spoonbill, Little Black Cormorant, Pied Cormorant, Australasian Darter, Magpie Goose, Caspian Tern and Whiskered Tern are recorded to breed in the system (Wetlands International unpublished data provided by R. Jaensch). Yellow Chat occurs in aggregations of tens if not hundreds of birds (R. Jaensch pers. comm. 2007). There are historical records of the vulnerable Australian Painted Snipe from the Lake Sylvester system, Brunette Creek and Playford River. Evidence suggests the Australian Painted Snipe may still occur at least occasionally in the IBA: suitable habitat for the species is abundant at Lake Sylvester and in 1993 a positive sighting was made at Lake Woods, in habitat similar to that which occurs at Lake Sylvester, and breeding was documented at Tarrabool Lake, which lies approximately 60 km north-west of the Lake Sylvester system (Jaensch 2003; R. Jaensch pers. comm. 2007).

Non-bird biodiversity: The Lake Sylvester system supports two plant species, Bergia barklyana and Goodenia cylindrocarpa, which are endemic to the Mitchell Grass Downs bioregion (Harrison et al. 2009). A number of plant and vertebrate species recorded in the system are largely confined to cracking-clay grasslands within the Mitchell Grass Downs bioregion (Fisher et al. 2002). Four plant species present in the system (Commelina tricarinata, Senecio depressicola, Iotasperma sessilifolium and Urochloa atrisola) have a restricted range within the Northern Territory (Harrison et al. 2009).